Numerous optical sensors are on the market today and find uses in many applications. Some of these uses include the automatic opening of doors, counting the movement of objects past a sensing point and the like. These optical sensors are usually integral packages including a light source and a light detecting transducer which generates a signal indicative of the presence or absence of an object or surface within the field of view of the transducer. The optical sensor typically generates a signal indicative of the presence or absence of an object or surface within the field of view of the transducer. The light source typically is a light-emitting diode and the transducer a phototransistor.
One of the problems which surrounds the optical sensors used today is the electrical variation that exists between different sensors. Thus, if a sensor goes bad and must be replaced, its response may be entirely different than that of the sensor that it replaces. To compensate for this variation, potentiometers have been used to vary either the light-emitting portion of the sensor or the sensitivity of the phototransistor to obtain the necessary result. This adjustment typically requires the presence of a technician thus increasing the cost and problems incumbent in the replacement of such sensors. It is far more desirable to have some means of automatically calibrating such sensors so that one sensor may be substituted for another without requiring further calibration. In this way the sensors can be replaced as simply as a light bulb in a socket.
Optical sensors are used extensively in connection with x-ray cassettes to sense whether or not an x-ray film is within the cassette or not and similarly whether or not a cassette has been doubly loaded with more than one sheet of film.